The field of the present invention involves the hydrothermal treatment of photolytically deposited metal and metal oxide films to favorably alter film characteristics at low temperatures for use in semiconductor manufacturing.
The semiconductor and packaging industries, among others, utilize conventional processes to form thin metal and metal oxide films in their products. Examples of such processes include evaporation, sputter deposition or sputtering, chemical vapor deposition (xe2x80x9cCVDxe2x80x9d) and thermal oxidation. Evaporation is a process whereby a material to be deposited is heated near the substrate on which deposition is desired. Normally conducted under vacuum conditions, the material to be deposited volatilizes and subsequently condenses on the substrate, resulting in a blanket, or unpatterned, film of the desired material on the substrate. This method has several disadvantages, including the requirement to heat the desired film material to high temperatures and the need for high vacuum conditions.
Sputtering is a technique similar to evaporation, in which the process of transferring the material for deposition into the vapor phase is assisted by bombarding that material with incident atoms of sufficient kinetic energy such that particles of the material are dislodged into the vapor phase and subsequently condense onto the substrate. Sputtering suffers from the same disadvantages as evaporation and, additionally, requires equipment and consumables capable of generating incident particles of sufficient kinetic energy to dislodge particles of the deposition material.
CVD is similar to evaporation and sputtering but further requires that the particles being deposited onto the substrate and undergo a chemical reaction during the deposition process in order to form a film on the substrate. While the requirement for a chemical reaction distinguishes CVD from evaporation and sputtering, the CVD method still demands the use of sophisticated equipment and extreme conditions of temperature and pressure during film deposition.
Thermal oxidation also employs extreme conditions of temperature and an oxygen atmosphere. In this technique, a blanket layer of an oxidized film on a substrate is produced by oxidizing an unoxidized layer which had previously been deposited on the substrate.
Several existing film deposition methods may be undertaken under conditions of ambient temperature and pressure, including sol-gel and other spin-on methods. In these methods, a solution containing a precursor compound that may be subsequently converted to the desired film composition is applied to the substrate. The application of this solution may be accomplished through spin-coating or spin-casting, where the substrate is rotated around an axis while the solution is dropped onto the middle of the substrate. After such application, the coated substrate is subjected to high temperatures which convert the film into a film of the desired material. Thus, these methods do not allow for direct imaging to form patterns of the amorphous film. Instead, they result in blanket, unpatterned films of the desired material. These methods have less stringent equipment requirements than the vapor-phase methods, but still require the application of extreme temperatures to effect conversion of the deposited film to the desired material.
In one method of patterning blanket films, the blanket film is coated (conventionally by spin coating or other solution-based coating methods; or by application of a photosensitive dry film) with a photosensitive coating. This photosensitive layer is selectively exposed to light of a specific wavelength through a mask. The exposure changes the solubility of the exposed areas of the photosensitive layer in such a manner that either the exposed or unexposed areas may be selectively removed by use of a developing solution. The remaining material is then used as a pattern transfer medium, or mask, to an etching medium that patterns the film of the desired material. Following this etch step, the remaining (formerly photosensitive) material is removed, and any by-products generated during the etching process are cleaned away if necessary.
In another method of forming patterned films on a substrate, a photosensitive material may be patterned as described above. Following patterning, a conformal blanket of the desired material may be deposited on top of the patterned (formerly photosensitive) material, and then the substrate with the patterned material and the blanket film of the desired material may be exposed to a treatment that attacks the formerly photosensitive material. This treatment removes the remaining formerly photosensitive material and with it portions of the blanket film of desired material on top. In this fashion a patterned film of the desired material results; no etching step is necessary in this xe2x80x9cliftoffxe2x80x9d process. However, the use of an intermediate pattern transfer medium (photosensitive material) is still required, and this is a disadvantage of this method. It is also known that the xe2x80x9cliftoffxe2x80x9d method has severe limitations with regard to the resolution (minimum size) that may be determined by the pattern of the desired material. This disadvantage severely limits the usefulness of this method.
It is thus evident that the conventional processes for the deposition of blanket films that subsequently need to be patterned invokes the need for several extra costly and difficult processing steps. However, some semiconductor applications, such as applications using a polymer-based substrate, are sensitive to the high temperatures typical in such conventional processes. Therefore a need exists for a low temperature deposition and patterning means of forming films in such applications.
While some of these methods are more equipment-intensive than others and differ in the use of either solution- or vapor-phase methods, such conventional processes for forming metal and metal oxide films is not optimal because, for example, they each require costly equipment, are time consuming, require the use of high temperatures to achieve the desired result, and result in blanket, unpatterned films where, if patterning is needed, further patterning steps are required. A desirable alternative to these methods would be the use of a precursor material that may be applied to a substrate and selectively imaged and directly photolytically patterned to form an amorphous film without the need for intermediate steps. Such films are herein referred to as a film deposited by photochemical metal organic deposition (PMOD(trademark) film), as described in U.S. Pat. No. 5,534,312, which is incorporated herein by reference in its entirety.
Such films may have a certain amount of porosity due to the existence of nanopores in the film matrix. The level of porosity is a factor of the process conditions used, as described in co-pending application entitled xe2x80x9cNanostructured and Nanoporous Film Compositions, Structures, and Methods for Making the Same,xe2x80x9d filed Sep. 30, 2002 and incorporated herein by reference in its entirety. As the porosity of such films increases, the density and permitivity decrease. In applications that require a high dielectric constant (k), including embedded capacitors for electronic packaging, future gate oxides for transistors in semiconductor devices, high-density dynamic random access memory (DRAM), piezoelectric micro-or nanoactuators, sensors and microwave tuning devices, this is not preferable. Additionally, in some applications it may be preferable to use crystalline, not amorphous films, such as when ferroelectric behavior is desired (e.g., use as a decoupling capacitor).
Conventional annealing methods that may be used to crystallize such films, also decrease the porosity of such films causing outgassing of the nanopores. However, the current and future industry needs have led to the use of polymer based electronic packaging substrates. Polymer based substrates cannot undergo conventional high temperature ( greater than 400xc2x0 C.) heat treatment needed to increase the density and dielectric constant of deposited films containing nanopores. The use of polymer based electronic packaging substrate will likely continue to increase due to cost and property reasons (e.g., flexibility, processing ease, variety of available polymers, substrate cost, availability in large areas).
Accordingly, there is a need for a method for the densification and/or the crystallization, into a nanocrystalline state, of PMOD(trademark) films in semiconductor applications sensitive to high temperature conventional processing methods, such as where polymer based electronic packaging substrates are used. In addition, there is a need for a directly photopatterned high dielectric constant (k) metal oxide thin films that combines the ease of spin-on coating and direct photo patterning of a dielectric and does not require high temperatures ( greater than 400xc2x0 C.) nor the use of plasma etching to achieve pattern definition.
Additionally, a need exists for a low temperature method of treating deposited films to remove residual organic species of the deposited PMOD(trademark) films.
To address those needs, processes for low temperature treatment of PMOD(trademark) films have been developed as methods of forming high dielectric metal and metal oxide films for use in semiconductor applications that are temperature sensitive.
The processes of the present invention can provide a directly patterned metal or metal oxide film with a high dielectric constant through low temperature processing( less than 300xc2x0 C.), thus replacing both the oxide and photoresist layers used in conventional surface imaging and ion implantation methods and allowing for the use of polymer based electronic packaging substrates. Another advantage of this invention is that the material which is produced has better etch resistance to plasma etching chemistries. A further advantage of this invention is that it facilitates the use of new materials for patterned layers, such as platinum, iridium, iridium oxide, ruthenium and ruthenium oxide, that are known in the art to be difficult or impossible to etch by conventional processes.
One embodiment of the present invention is a method of forming PMOD(trademark) films with a high dielectric constant comprising the steps of:
selecting at least one high k precursor material, such as barium titanate or barium strontium titanate (BST);
forming a layer comprising the precursor atop a substrate;
converting at least a portion of the precursor layer;
developing the precursor layer thereby forming a pattern in the precursor layer;
transferring the pattern to the substrate, whereby a photoresist is not used in forming the pattern;
hydrothermally treating the PMOD(trademark) film to increase the dielectric constant of the film; and
thermal annealing at xcx9c400xc2x0 C.
The unconverted portion of the precursor layer can be developed away an with an appropriate developer. Alternatively, the converted portion of the precursor layer can be developed away an with a developer. The developer can be a liquid developer comprising at least one alcohol and at least one ketone, wherein the total volume of all of the alcohols present is greater than 50% of the sum of the volumes of all of the alcohols present plus the volumes of all of the ketones present in the liquid developer. Preferably, at least one alcohol of the developer is isopropyl alcohol (IPA), the at least one ketone is methyl isobutyl ketone (MIBK), and the ratio of IPA:MIBK is from about 1:1 by volume to about 1:40 by volume. A second preferred developer compound is IPA:Hexane, and the ratio of IPA:Hexane is from about 1:1 by volume to about 1:40 by volume.
Another embodiment of the present invention is a method of forming PMOD(trademark) films with a high dielectric constant comprising the steps of:
selecting at least one high k precursor material;
forming a layer comprising the unconverted precursor on the substrate;
blanket converting unconverted precursor layer;
hydrothermally treating the PMOD(trademark) film to increase the dielectric constant of the film; and
themal annealing at 400xc2x0 C.
Herein, the hydrothermal treatment step will alternately be referred to as the xe2x80x9cphotoconversionxe2x80x9d process, which in the present invention represents the degree of transformation of the photoactive metal-organic precursor films to dense amorphous or chrystalline metal oxide films, free of organic species and free of nanoscale voids.
Conversion can be accomplished with an energy source selected from light, electron beam irradiation, ion beam irradiation, and mixtures thereof Ions can be implanted by exposing the uncovered substrate to an ion beam.
In each embodiment of the invention, a preferred precursor material is a metal complex comprising at least one ligand selected from the group consisting of acac, carboxylato, alkoxy, azide, carbonyl, nitrato, amine, halide, nitro, and mixtures thereof and at least one metal selected from the group consisting of Li, Al, Si, Ti, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Ba, La, Pr, Sm, Eu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Pb, Th, U, Sb, As, Ce, Mg, and mixtures thereof. The selected precursor solution is mixed in a solvent and deposited on a substrate, which is subsequently converted, for example by UV radiation for photolysis.
Most preferably the metal complex is selected such that a high k PMOD T film results. Examples of such resulting PMOD(trademark) films are barium titanate (BT), lead zirconate titanate (PZT), titanium oxide, and barium strontium titanate (BST).
The hydrothermal treatment of the resulting PMOD(trademark) films increases the density by reducing the porosity of the film and can crystallize the film under selected conditions. Hydrothermal treatment also allows for the formation of low stress films substantially free from residual organic species. These results are achieved at low process temperatures ( less than 400xc2x0 C.).